As part of studies aimed at improving the methodology for hollow fiber cell culture and investigating the response of cultured cells to pharmacologic agents, instrumentation systems are being developed for measuring relevant parameters. Under current development are systems for monitoring the rate of oxygen consumption and the extracelluar oxygen partial pressure. The instruments employed are a mass spectrometer and miniature noble metal oxygen electrodes. The latter may be operated in either voltaic or amperometric (polarographic) modes. Subsequent parameters to be investigated are pH and carbon dioxide partial pressure. Cell lines employed in the cultures are rat pituitary cells (GH1) and human choriocarcinoma cells (JEG-7).